A synergistic heterojunction of SnS2/SnSSe nanosheets on GaN for advanced self-powered photodetectors

Tin-based TMDCs are gaining traction in optoelectronics due to their eco-friendliness and easy synthesis, contrasting Mo/W-based counterparts. This study pioneers the solvothermal synthesis of highly crystalline SnSSe alloy, akin to Janus structures, bridging a notable research gap. By integrating SnS2/SnSSe materials onto a GaN platform, a synergistic heterojunction is created, enhancing light absorption and the electron-hole pair separation efficiency, demonstrating a self-powered photodetection. The GaN/SnS2/SnSSe heterojunction showcases a staircase-like (type-II) band alignment and exceptional performance metrics: high photoresponsivity of 314.96 A W-1, specific detectivity of 2.0 × 1014 jones, and external quantum efficiency of 10.7 × 104% under 365 nm illumination at 150 nW cm-2 intensity and 3 V bias. Notably, the device displays intensity-dependent photocurrent and photoswitching behaviors without external bias, highlighting its unique self-powered attributes. This study underscores SnS2's significance in optoelectronics and explores SnSSe integration into van der Waals heterostructures, promising advanced photodetection devices and bias-free optoelectronics.

Giant In-Plane Flexoelectricity and Radial Polarization in Janus IV-VI Monolayers and Nanotubes

Nanotubes have established a new paradigm in nanoscience because of their atomically thin geometries and intriguing properties. However, because of their typical metastability compared to their 2D and 3D counterparts, it is still fundamentally challenging to synthesize nanotubes with controlled size. New strategies have been suggested for synthesizing nanotubes with a controlled geometry. One of these is considering Janus 2D layers, which can self-roll to form a nanotube. Herein, we study 412 nanotubes (along the armchair and zigzag directions) based on 36 Janus IV-VI compounds using density functional theory (DFT) calculations. By investigating the energy-radius relationship using structural models and Bayesian predictions, the most stable nanotubes show negative strain energies and radii below 20 Å, where curvature effects can play a significant role. The band structures show that the selected nanotubes exhibit sizable band gaps and size-dependent electronic properties. More strikingly, the flexoelectricity along the in-plane directions and radial directions in these nanotubes is significantly larger than that in other nanotubes and their 2D counterparts. This work opens up an avenue of structure-property relationships of Janus IV-VI nanotubes and demonstrates giant flexoelectricity in these nanotubes for future electronic and energy applications.

Flexible Memory Device Composed of Metal-Oxide and Two-Dimensional Material (SnO2/WTe2) Exhibiting Stable Resistive Switching

Two-terminal, non-volatile memory devices are the fundamental building blocks of memory-storage devices to store the required information, but their lack of flexibility limits their potential for biological applications. After the discovery of two-dimensional (2D) materials, flexible memory devices are easy to build, because of their flexible nature. Here, we report on our flexible resistive-switching devices, composed of a bilayer tin-oxide/tungsten-ditelluride (SnO2/WTe2) heterostructure sandwiched between Ag (top) and Au (bottom) metal electrodes over a flexible PET substrate. The Ag/SnO2/WTe2/Au flexible devices exhibited highly stable resistive switching along with an excellent retention time. Triggering the device from a high-resistance state (HRS) to a low-resistance state (LRS) is attributed to Ag filament formation because of its diffusion. The conductive filament begins its development from the anode to the cathode, contrary to the formal electrochemical metallization theory. The bilayer structure of SnO2/WTe2 improved the endurance of the devices and reduced the switching voltage by up to 0.2 V compared to the single SnO2 stacked devices. These flexible and low-power-consumption features may lead to the construction of a wearable memory device for data-storage purposes.